1. Field of the Invention
The present invention relates to a method and apparatus for pumping or delivering fluids utilizing a flexible vessel that may be subject to controlled pressures and preferably located within a pressure vessel.
2. Description of the Prior Art
Current methods for pumping or delivering fluids, particularly biological fluids, include utilizing peristaltic (tubing) pumps, diaphragm pumps, and centrifugal pumps. Biological fluids encompass fluids that comprise, exist in or are used in or delivered to living organisms. Indeed, biological fluids may comprise pharmaceutical preparations (e.g., insulin, erythopoietin, or morphine) or biological preparations (e.g., liposomes, plasmids, naked DNA or transformed cells), bodily fluids and their components, such as blood cells, and other fluids that comprise biological components, including living organisms such as bacteria, cells or other cellular components. Biological fluids also may comprise whole blood or specific whole blood components, including red blood cells, platelets, buffy coat, white blood cells, precursor cells, progenitor cells; prokaryotic and eukaryotic cell suspensions, including recombinant, transformed, and transfected cells; viruses and viral preparations including recombinant viruses; membrane vesicle preparations, including lysosomes, endosomes, caveolae, micelles, and liposomes; molecule interactions including DNA-protein, RNA-protein, and protein-protein interactions; DNA preparations; RNA preparations; and protein preparations.
Certain fluid types, such as fluids comprising pressure or flow sensitive fluids, such as biological fluids, can be negatively affected by subjecting such fluids to such current pumping or delivering methods. For example, biological fluids comprising blood or its cellular components, may be damaged (e.g., cells may be lysed or membranes damaged) when exposed to perturbations and/or turbulence caused by such current methodologies. Moreover, these fluid types may also be negatively affected by inaccurate or inconsistent flow rates and pressures created by such current methods. In addition, drug delivery systems are negatively affected by such inaccurate or inconsistent flow rates.
One of the specific drawbacks, for example, with peristaltic pumps is that they are essentially positive displacement and have the potential to develop excessive pressures if an occlusion occurs within the pump or its components. When pumping or delivering biological fluids, such as whole blood or buffy coat, any excess pressure resulting from even a partial occlusion may result in cell membrane damage or hemolysis. Diaphragm pumps present difficulties in the measurement of fluid volume pumped when partial strokes are involved and may require auxiliary valving. Centrifugal pumps are difficult to track for volume pumped, cannot hold against a static head without check valves, are non-reversible, and generally require some mechanical rotor support in the fluid stream (e.g., a hydrodynamic bearing or magnetic system). The diaphragm and centrifugal pump types also have more complex disposable elements than the peristaltic type pumps. In the drug delivery area, devices such as the hypodermic syringe that deliver a bolus of a drug or other active agent also present difficulties since the bolus must be gradually absorbed and delivered throughout the patient's body, which is a process subject to many individual variances.
The Kamen family of pump technology (e.g., U.S. Pat. Nos. 4,600,401, 4,778,451, 4,808,161, and 5,193,990) in some respects attempt to solve some of the problems of the peristaltic pump, however, Kamen-type pumps have their own drawbacks. Kamen described a fluid movement technology based on the use of pneumatically driven diaphragm pumps and valves controlled by computer calculations of stroke volume displacement as a function of pressure and temperature. These calculations are time consuming and necessarily precise because the stroke volumes are small and the cumulative error must be kept minimal. Each stroke is interrupted by a long static period during which these measurements are made. In order to maintain the required average flow rate, the actual flow rate must be high, resulting in a step type of flow (a jump up when restarting the flow) which is detrimental, for example, to sensitive fluids in general, to many biological fluids, and to most types of cell separation processes, particularly the “skimming” type cell separation processes commonly used in conjunction with centrifuges. (In a skimming operation, discontinuous flow and the jump of restarting flow, for example, in a photopheresis process, disturbs cell separation causing a flood of red blood cells in a plasma stream.) To compensate for the inefficiencies caused by discontinuous flow in a system using a Kamen-type pump, and its impact on, for example, a separation type process, additional fluid flow must be processed and procedure times increased.
Additionally, the Kamen family of pump technology requires a rigid disposable pumping or delivering/valving module which contains valve chambers that interrupt the laminar nature of flow in tubing, causing undesired mixing of separated components as the front flows through. This module (or cassette) is also typically costly and complicated to manufacture.
The present invention differs from the prior art, in that it allows, for example, for pressurized flow of a fluid without a pause in pumping or delivering. The present invention, in contrast to the Kamen pump family described above, allows, for example, for one continuous flow (i.e., “push”) of fluid. The costly and complicated Kamen disposable pump/valve is eliminated. The present invention can be operated at much higher constant flow rates and average flow rates without the risk of high restart flow introduced in the Kamen system, as well as others, to catch up the average flow rate due to the pause and its related reduction in flow rate. The discontinuity and inefficiencies of the Kamen-type system and others are, therefore, addressed by the present invention.
Additionally, the present invention, in contrast to the centrifugal type pump, is or can be configured to be reversible. The present invention can also operate at a constant or modulated pressure to avoid the potential inherent in the peristaltic and other types of pump systems to develop excessive pressures, for instance, during an occlusion of the flow. The volume and other parameters of the fluid flow are accurately measurable in the present invention, in contrast to the diaphragm and centrifugal-type pump systems. The present invention may include, for example, a pressure limiting pump or direct weight measurement rather than a flow rate controlled pump, for added safety if a line associated with the pump becomes blocked or occluded. The present invention can also incorporate a minimal amount of noncomplex disposable elements and yet maintain, if desirable, the sterility of the pumping or delivering operation. Such sterility and minimized complexity may be particularly desirable when manipulating biological fluids such as pharmaceuticals and other active agents.
In comparison to pumps presently utilized in known processes or treatments, for example, the photopheresis and peritoneal dialysis processes described infra, the present invention can, for example: reduce total treatment or process time; reduce irradiation time (for photopheresis); allow increased flow rate; increase the total number of target cells collected or separated per total target cells processed (i.e., yield); increase the total number of target cells collected per treatment or process time; increase the total target cells collected per total volume of processed biologic fluid; reduce cell, fluid or fluid element damage in the process (e.g., reduced hemolysis); reduce contamination of target items collected (e.g., increase the percentage of target cells collected per total cells collected); operate with a reduced pressure differential; and, reduce flow rate differential.